Tapered Composite Stringers for Delamination Control
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Solution Overview
Problem
Conventional carbon fiber reinforced polymer (CFRP) stringers fail in curved, high-load areas of aircraft due to interlamina tension stress and delamination, necessitating heavy and complex metallic spliced joints to prevent failure.
Innovation Solution
Continuous composite stringers with tapered webs and widening base flanges are used, coupled with reinforcement fittings, to manage loads and moments in curved regions without delamination, maintaining a constant cross-sectional area and reducing weight and part count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional CFRP stringers are used in curved high-load areas, then the stringers are lightweight and strong, but they fail due to interlamina tension stress and delamination
Solution Approach 1:
The patent applies local quality by varying the web thickness and base flange width along the stringer length. The web is thickest at the ends and thins toward the center, while the base flange widens in curved regions. This non-uniform geometry distributes stresses appropriately, with thicker sections handling higher loads at ends and wider flanges providing reinforcement at curved regions prone to delamination.
Solution Approach 2:
The patent utilizes composite materials by bonding a CFRP noodle between the stringer web and base flange to prevent delamination. Additionally, metal reinforcement plates are applied to the outer surface of the base flange in curved regions, creating a hybrid composite-metal structure that enhances reliability while maintaining the lightweight benefits of CFRP.
2Reliability
If metal spliced joints with SOB skin splice plates are used to prevent stringer failure, then delamination is prevented, but the structure becomes heavy and complex
Solution Approach 1:
Rather than using heavy metal spliced joints throughout, the patent applies reinforcement locally only where needed. The CFRP noodle is bonded throughout the stringer length, and metal reinforcement plates are applied only to the outer surface of the base flange in curved high-load regions, minimizing additional weight while providing reliability where most needed.
Solution Approach 2:
The patent maintains the lightweight advantage by primarily using CFRP materials. The CFRP noodle bonded between web and flange provides delamination prevention without the weight penalty of full metal construction. Metal reinforcement plates are used sparingly only in critical curved regions, creating a hybrid structure that balances reliability with weight efficiency.
3Weight of moving object
If continuous CFRP stringers are used in curved regions, then weight and part count are reduced, but the stringers cannot withstand out-of-plane kick loads and rolling moments
Solution Approach 1:
The patent addresses load capacity in curved regions by implementing local quality variations. The base flange is widened specifically in curved regions to increase moment of inertia and load capacity where needed, while maintaining standard dimensions in straight regions to minimize weight. This selective reinforcement provides adequate strength without the weight penalty of uniformly thick stringers.
Solution Approach 2:
The patent enhances load capacity by bonding a CFRP noodle between the web and base flange, which prevents delamination and maintains structural integrity under out-of-plane kick loads. Additionally, metal reinforcement plates are applied to the outer surface of the base flange in curved regions, creating a hybrid composite-metal structure that withstands rolling moments and other high loads while remaining lighter than full metal construction.
Data Source
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AI summary
Apparatus and methods provide for utilizing continuous curved composite stringers to control the loads and corresponding moments within curved regions of an aircraft or other vehicle without delamination or other interlamina failures. According to embodiments described herein, any number of tapered height curved composite stringers may be coupled to continuous skin components to create a curved continuous panel. The tapered height curved composite stringers may have webs that taper to a reduced height within curved regions and corresponding base flanges that widen during web tapering. Reinforcement fittings may be coupled to the base flanges in the curved regions for further strengthening and to provide for the attachment of supplemental panels to the stringers.